Ia Afferent input alters the recruitment thresholds and firing rates of single human motor units

Vibration of the patellar tendon recruits motor units in the knee extensors via excitation of muscle spindles and subsequent Ia afferent input to the α-motoneuron pool. Our first purpose was to determine if the recruitment threshold and firing rate of the same motor unit differed when recruited involuntarily via reflex or voluntarily via descending spinal pathways. Although Ia input is excitatory to the α-motoneuron pool, it has also been shown paradoxically to inhibit itself. Our second purpose was to determine if vibration of the patellar tendon during a voluntary knee extension causes a change in the firing rate of already recruited motor units. In the first protocol, 10 subjects voluntarily reproduced the same isometric force profile of the knee extensors that was elicited by vibration of the patellar tendon. Single motor unit recordings from the vastus lateralis (VL) were obtained with tungsten microelectrodes and unitary behaviour was examined during both reflex and voluntary knee extensions. Recordings from 135 single motor units showed that both recruitment thresholds and firing rates were lower during reflex contractions. In the second protocol, 7 subjects maintained a voluntary knee extension at 30 N for approximately 40–45 s. Three bursts of patellar tendon vibration were superimposed at regular intervals throughout the contraction and changes in the firing rate of already recruited motor units were examined. A total of 35 motor units were recorded and each burst of superimposed vibration caused a momentary reduction in the firing rates and recruitment of additional units. Our data provide evidence that Ia input modulates the recruitment thresholds and firing rates of motor units providing more flexibility within the neuromuscular system to grade force at low levels of force production. Electronic Publication     

Differences in the activation of m. biceps brachii in the control of slow isotonic movements and isometric contractions

Summary We have compared muscle activation in the control of slow isotonic movements and isometric contractions. Specific attention has been given to the contribution of the two force-grading mechanisms, the recruitment of motor units and the modulation of firing frequency in motor units that have already been recruited. The recruitment order of the m. biceps motor units under study was the same during isometric contractions and slow isotonic movements. However, the recruitment thresholds of the m. biceps units were considerably lower for both isotonic flexion and extension movements, even at velocities as low as 2 deg/s, than for isometric contractions. Furthermore, firing frequency at recruitment was found to depend on the motor task: at recruitment the motoneurone starts firing with a higher firing frequency during isotonic flexion movements and a lower firing frequency during isotonic extension movements than during isometric contractions. Two main conclusions can be drawn from these results. First of all, the concept of one single activation parameter (total synaptic drive?) cannot account for the motor-unit behaviour observed during our experiments: the relative contribution of the two forcegrading mechanisms is different for different tasks. Secondly, the distribution of activity among flexor motoneurone pools is different for isometric contractions and isotonic movements.     

Sensitization of nociceptive cutaneous nerve fibers from the rat's tail by noxious mechanical stimulation

Summary This single fiber study on rat tail nerve afferents attempts to establish a peripheral neural correlate for the hyperalgesia to mechanical stimulation which follows injury to the skin. Mechano-heat sensitive C fibers (MH-C or polymodal nociceptors) and high-threshold mechanoreceptive A delta fibers (HTM-A delta) were examined with a series of constant noxious pressure stimulations (4-6-8-4 N on 25 mm², 120 s each, 5 min intervals). These injurious stimuli were either directed to the most sensitive spot of the receptive fields (central stimulation) or closely outside their borders (1–5 mm). With this protocol no clear sensitization was seen in MH-C fibers apart from a stronger dynamic response to central stimulation in some of them. In contrast, most HTM-A delta units, irrespective of the site of noxious stimulation, developed spontaneous activity, lowering of their von Frey thresholds and expansion of their receptive fields. All HTM-A delta units responded to outside stimulation: upon the first stimulus (4 N) there was a delayed discharge of continuously increasing frequency (recruited response), but the onset of the last stimulation (4 N repeated) evoked vigorous dynamic responses in many fibers. The recruitment of HTM-A delta nociceptor activity may contribute to post-injury hyperalgesia to mechanical stimulation and it may counteract adaptation of the single afferent fiber during prolonged noxious influence.On leave from the Laboratoire de Physiologie, Faculté de Médecine Lyon-Sud, Chemin du Petit Revoyet, F-69600 Ouillins, France     

Classes of Auditory Evoked Responses

Auditory evoked potentials arise from different neural structures, yield different types of information and suffer different limitations. In order of activation, these are

(1) Organ of Corti (0 msec latency): 'CM'; usefulness uncertain.

(2) Auditory nerve (1–4 msec): 'N₁'; practically limited to study of basal turn (high frequencies). Basis of electrocochleography; useful for certain abnormalities but not for threshold audiogram.

(3) Cochlear nucleus through inferior colliculus (3–20 msec): low voltage waves demonstrated but not clearly identified with structures.

(4) Medial geniculate and primary cortical projection area (25–50 msec): low voltage waves can yield a threshold audiogram and are stable in sleep. Inadequately exploited.

(5) Cortical projection areas; secondary response (50–280 msec): 'V potential': a slow, variable on- or off-response, but excellent for threshold audiograms in cooperative waking subjects. A DC shift during continued stimulation has also been demostrated but not exploited.

(6) Diffuse late cortical responses: a) sleep (180 msec or more): several forms including the K complex. The forms, voltage and threshold vary with the stage of sleep. Threshold audiometry is difficult and not very precise; b) awake (300 msec or more): P₃₀₀ and CNV are both related to 'expectancy' and can be combined with conditioning to test certain psychological functions.     

Neurophysiological adaptations to spaceflight and simulated microgravity

Changes in physiological functions after spaceflight and simulated spaceflight involve several mechanisms. Microgravity is one of them and it can be partially reproduced with models, such as head down bed rest (HDBR). Yet, only a few studies have investigated in detail the complexity of neurophysiological systems and their integration to maintain homeostasis. Central nervous system changes have been studied both in their structural and functional component with advanced techniques, such as functional magnetic resonance (fMRI), showing the main involvement of the cerebellum, cortical sensorimotor, and somatosensory areas, as well as vestibular-related pathways. Analysis of electroencephalography (EEG) led to contrasting results, mainly due to the different factors affecting brain activity. The study of corticospinal excitability may enable a deeper understanding of countermeasures' effect, since greater excitability has been shown being correlated with better preservation of functions. Less is known about somatosensory evoked potentials and peripheral nerve function, yet they may be involved in a homeostatic mechanism fundamental to thermoregulation. Extending the knowledge of such alterations during simulated microgravity may be useful not only for space exploration, but for its application in clinical conditions and for life on Earth, as well.     

Challenges and Potential Solutions for Recruitment and Retention of Hematopoietic Cell Transplantation Physicians: The National Marrow Donor Program’s System Capacity Initiative Physician Workforce Group Report

Hematopoietic cell transplantation (HCT) remains the only known curative therapy for many patients with hematologic, metabolic, and immunologic disorders. Furthermore, the use of HCT has increased with the emergence of HCT as a viable therapeutic option for older patients, those with significant comorbidities, and, with the demonstrated clinical effectiveness of alternative allogeneic donor sources, for those patients without a suitable sibling donor. The National Marrow Donor Program (NMDP) estimates that by 2020, it will facilitate 10,000 transplantations per year, double the number in 2010. To understand the needs of the HCT infrastructure to facilitate this number of transplantations, the NMDP organized the System Capacity Initiative 2020, centered on 6 working groups representing a diverse group of stakeholders. The Physician Workforce Group was tasked with addressing issues relating to recruitment and retention of transplantation physicians. We report here the results of our efforts and future initiatives.     

The use of multi-national web surveys for comparative analysis: Lessons from the European Web Survey on Drugs

BackgroundMost comparative drug policy analyses utilise measures of drug use, often from general population surveys (GPS). However, the limitations of GPS are well-recognised, including the small numbers of people who use illicit drugs sampled. Web surveys offer a potential solution to such issues. Therefore EMCDDA conducted a study to assess the potential for using such surveys to supplement information obtained from GPS.MethodsThe European Web Survey on Drugs (EWSD) asked about use of cannabis, amphetamines, cocaine and MDMA in 14 countries from 2016 to 2018. Each participant country translated the questionnaire as necessary and devised its own sampling strategy. Individuals aged 18+, resident in the participant country, who had used one or more of the drugs covered by the survey in the past 12 months were included in the analysis. Participation was anonymous and voluntary.ResultsMore than 40,000 people completed the survey, with recruitment mostly through social media. Larger samples of users of all drug types than found in GPS were generally obtained. However, the respondent profiles differed markedly between countries, e.g. the proportion aged 18–24 ranged from 30% to 80%. The results relating to use showed both inter-country similarities and differences, e.g. mean daily amounts of cocaine used varied between countries but increases in amounts used with increased frequency of use were similar. Price data showed good external validity.ConclusionWeb surveys offer the possibility of collecting information from large numbers people who use illicit drugs quickly and cheaply and can fill important gaps in our knowledge of patterns of use, particularly by recreational users. However, they also have limitations. Standardising questionnaires and approaches to data cleaning and analysis facilitates comparisons between countries but obtaining comparable samples may be challenging. Multinational surveys need to balance standardisation of methods with responsiveness to differing country contexts; our collaborative model does this.     

Self-management tasks to improve mobility and reduce fall risk are not leading to lower research participation in older adults

Purpose of studyThe first aim is to evaluate, in a sub-study, the recruitment process of the Senior Step Study, which was an intervention study on the self-management of mobility and fall risk; the second aim is to explore the reasons mentioned by older people, from three different settings, for (not) participating.MethodsSubjects were community-dwelling older persons, residents of homes for the elderly, and older persons regularly visiting community centres. The effectiveness of different recruitment procedures was analysed for each setting separately. We also analysed reasons for accepting and declining participation between the settings.ResultsThe total inclusion rate was 27.9%. A personal initial approach (i.e., first contact was face-to-face or in a group meeting) did not improve the inclusion rate. More subjects consented to participate after an introductory meeting (which was planned after the first face-to-face contact) compared to persons not having one (p < 0.01). At different settings, subjects gave different reasons for participation. No differences were found in the reasons for refusing participation. Especially in homes for the elderly, people refused to participate because the research was too burdensome.ConclusionsThe inclusion rates in this study are comparable to other self-management studies with older people. An introductory meeting during which the study design and benefits of participating are explained and formal interim evaluations of the recruitment process may benefit recruitment. Recruiting older persons for self-management tasks is possible with the appropriate recruitment process, enabling more research on this increasingly important research topic.     

个人-组织匹配测量在员工选拔中的应用展望

本文回顾了个人-组织匹配的概念由来和相关研究,总结了个人-组织匹配对于员工态度和行为等结果变量的影响,介绍了将个人-组织匹配与员工选拔相结合的新招聘模式,并对该模式的具体程序、可行性及存在的障碍进行了探讨。     

Significance of the SISI Test and Its Relation to Recruitment

Auditory brainstem responses (ABR) evoked by clicks allow a threshold evaluation for the high-frequency range (2-4 kHz) but not for middle and low frequencies (0.5-1 kHz). In 19 normally hearing subjects aged between 24 and 40 years, ABRs have been recorded using clicks and 0.5- and 1-kHz tone pips, with durations of 6 and 3 ms, respectively, and rise-decay times of 3 and 1.5 ms. The input signal was filtered by a passband filter of 20-5000 Hz. Parameters of tracings elicited by the different kinds of stimuli are compared. Tone-pip ABR morphology does not show the conventional seven peaks but a single large vertex-positive wave. On the ascending branch high-frequency potentials, probably corresponding to the I, II, III and IV-V click-evoked peaks, were visible in some cases, but they rapidly disappeared as the stimulus intensity was decreased. Their 2.3-3 ms greater mean latency values are presumably related to the rise times of the stimuli employed. In terms of bioelectric generators, this large vertex-positive peak probably corresponds to the Jewett V wave. It probably represents a generalized asynchronous dendritic activity. Thus it is possible to obtain ABRs to middle- and low-frequency stimuli. Mean amplitude values of the slow wave are considerably higher than those of the Jewett V wave, but standard deviations are also larger. The positive wave has been identified in response to 1-kHz tone pips in 100% of cases at 30 dB nHL and in 52% of cases at 20 dB, while for 0.5-kHz tone pips in 73.7% of cases at 30 dB and in 57% at 20 dB. On the whole the threshold is located between 15 and 30 dB nHL.

L'étude des potentiels auditifs du tronc cérébral évoqués par des clics permet une évaluation objective du seuil auditif dans le domaine des hautes fréquences (2-4 kHz), mais pas dans celui des fréquences moyennes et basses (0, 5-1 kHz).

Nous avons étudié, chez 19 sujets normo-entendants aˇgés de 24 à 40 ans, les potentiels auditifs du tronc cérébral évoqués par des clics et des pips tonaux de 0,5 et 1 kHz, la durée des pips tonaux étant respectivement de 6 et 3 ms, avec un temps de montee de 3 et 1,5 ms.

Le signal était filtré avec une bande passante de 20-5000 Hz. Nous avons ainsi comparé les paramètres des tracés obtenus avec ces différents types de stimulus et trouvé que les pips tonaux n'évoquaient pas l'apparition des sept pics conventionnels, mais seulement une onde assez ample, positive au vertex; parfois, il est possible de reconnaiˇtre sur sa branche ascendante la présence de potentiels à haute fréquence qui correspondent selon toute probabilité aux pics I, II, III et IV-V évoqués par des clics. Leur amplitude décroiˇt et ils disparaissent lorsqu'on diminue l'intensité de la stimulation. Les latences de cette onde ample, positive au vertex, supérieures de 2,3-3 ms à celles de l'onde V de Jewett, sont probablement liées au temps de montée du stimulus employé. En termes d'origine bioélectrique, cette onde correspond vraisemblablement à celle du pic V de Jewett. Elle semble représenter une activité dendritique, asynchrone. On peut done obtenir des potentiels auditifs du tronc cérébral avec des stimuli de basse et de moyenne fréquence. Les amplitudes moyennes de cette onde sont beaucoup plus importantes que celles du pic V de Jewett, mais les déviations standard sont aussi plus grandes. Cette onde est présente dans 100% des cas pour les pips tonaux de 1 kHz à 30 dB nHL et dans 52% à 20 dB, tandis qu'elle est présente dans 73,7% des cas à 30 dB et dans 57% à 20 dB lorsque on emploie des pips tonaux de 0,5 kHz. Les seuil objectif se situe ainsi entre 15 et 30 dB nHL.